JLKP 1.4

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1.4 Sea-Floor Spreading

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Vocabulary:

Mid-Ocean Ridge-the longest chain of mountains in the world
Sonar-a device that bounces sound waves off underwater objects and then records the echoes of these sound waves
Sea-Floor Spreading-the process that continually adds nes material to the ocean floor
Deep-Ocean Trenches-deep underwater canyons where the ocean floor plunges; forms where the oceanic crust bends downward
Subduction-the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle
Outline:
  • Mapping the mid-ocean ridge----

    • Sonar is used to map the ocean floor
    • Evidence for Sea-Floor Spreading
    • Harry Hess studied mid-ocean ridge and thought of sea floor as a conveyor belt at mid-ocean ridge, molten material rises from the mantle and erupts; molten material spreads out, pushing older rock to both sides of ridgeand cools down
  • Evidence from Molten Material----

    • scientists found strange rocks shaped like toothpaste squeezed from a tube only forms from when molten material hardens quickly after erupting underwater
  • Evidence from Magnetic Stripes----

    • Earth's magnetic poles reversed themselves stripes going north and south side by side patterened
  • Evidence from Drilling Samples----

    • used Glomar Challenge to dig up samples found that farther frm the ridge=older rock and closer to ridge= newer rock
  • Subduction at Deep-Ocean Trenches----

    • at deep ocean trenches, subduction allows floor to sink into mantle
  • Subduction and Earth's Oceans----

    • subduction and sea-floor spreading can change the size and shape of the ocean
  • Subduction in the Pacific Ocean
    ----

    • Pacific Ocean many deep trenches for subduction- floor getting smaller
  • Subduction in the Atlantic Ocean
    ----
    • Atlantic Ocean has little shallow trenches for subduction- floor has nowhere to go; floor gets bigger